1. Field of the Invention
This invention relates to electronic circuits, and more particularly, to the distribution of power to electronic circuits.
2. Description of the Related Art
With each new generation of computer systems, performance demands increase. One such demand relates to power distribution systems, which are required to supply increasing currents at lower voltages and lower impedances. These demands make design of a power distribution system increasingly difficult.
In many computer systems, processors and application specific integrated circuits (ASICs) are the chief consumers of power. Power is typically delivered to these components through a printed circuit board (PCB). Power distribution to a processor or ASIC can consume a significant portion of PCB resources, and is but one of several competing demands which must be considered during the PCB""s design. Other demands include signal distribution and routing, component mounting, connector mounting, and so on. These demands are often times in conflict with one another, and thus compromises must be made to the design of the PCB. Such compromises may result in a less than optimal solution in addressing some or all of these demands.
Power distribution on a PCB typically involves at least one pair of copper planes (a power plane and a ground plane), along with a number of decoupling capacitors, typically mounted on a surface of the PCB. Since the PCB must also accommodate signal traces for a number of signals, the copper planes are often times perforated by holes known as vias. The presence of these signal vias may have a tendency to increase the inductance of the copper planes, which in turn results in an increase in impedance. Inductive impedance can be expressed by the formula Z=2xcfx80fL, wherein Z is the impedance, f is the frequency, and L is the inductance. Thus, the impedance of the power distribution system may be affected in large part by both the number of signal vias, as well as the frequency at which the computer system is designed to operate.
Further compounding problems of power distribution on a PCB is the fact that many computer systems required different voltages for various components. This may increase the number of copper planes needed for power distribution, as each voltage may require a separate power plane, and often times will have a separate ground plane as well. This may further increase the number of vias necessary in the PCB, thereby increasing the inductance of each of the power planes.
The problems outlined above may be solved in large part by a system and method for distributing power to an integrated circuit. In one embodiment, a power laminate may be mounted to a printed circuit board (PCB). The integrated circuit for which power is to be distributed may be electrically coupled to the PCB. The power laminate may include one or more power planes and one or more reference (i.e. ground) planes, with each pair of power/reference planes separated by a dielectric layer. The power laminate may also include a connector or other means for receiving power from an external power source. The power laminate may be electrically coupled to the integrated circuit, thereby enabling it to provide core power to the integrated circuit. The power laminate may also include a voltage regulator circuit, and a plurality of decoupling capacitors. In one embodiment, the power laminate may include a plurality of apertures which allow for the passing of connections between the integrated circuit and the PCB. The integrated circuit may be mounted to the PCB by solder balls of a ball-grid array, elestomeric connections of a land-grid array, or other type of mounting. The each of the solder balls or elastomeric connections may pass though one of the apertures of the power laminate.
The PCB may include a signal layer for conveying signals to and from the integrated circuit, but does not include any means for directly providing core power to the integrated circuit. Thus, all core power provided to the integrated circuit may be supplied by the power laminate. However, the PCB may include one or more pair of copper planes (e.g. a pair including a power plane and a reference plane) for providing power to other components mounted upon the PCB.
As used herein, the term xe2x80x9ccore powerxe2x80x9d refers to that power having a specific voltage and a specific current that is supplied to the integrated circuit itself. For example, one embodiment of an integrated circuit may require a core power having a voltage of 1.2 volts and a maximum current of 20 amperes. The PCB may be configured for providing power to other components mounted upon it. In one embodiment, the integrated circuit may require power at a low voltage, such as 1.2 volts, for high-frequency operation, while other components mounted upon the PCB which operate at a lower frequency may be configured to receive power with a higher voltage, such as 5 volts. One embodiment of the power laminate having a voltage regulator may be configured to receive power from the PCB to which it is mounted, whereupon the voltage regulator may convert this power into the core power required by the integrated circuit. In another embodiment, the power laminate (and thus the voltage regulator, if present) may be configured to receive power from a source separate from the PCB.
In one embodiment, a power laminate may be mounted on the bottom of a PCB, with the integrated circuit mounted on top. The power laminate and the integrated circuit may be attached to the PCB by soldering, and one or both may include an array of solder balls known as a ball-grid array. Alternatively, the power laminate may include a land-grid array, in lieu of a BGA, for mounting it to the PCB.
In another embodiment, the power laminate may be arranged between the integrated circuit and the PCB. The power laminate may have at least one aperture to allow the passage of signals between the PCB and the integrated circuit.
The power laminate may include a voltage regulator circuit. The voltage regulator circuit may be implemented with either discrete components or with a voltage regulator module. In one embodiment, the voltage regulator may be a switching voltage regulator. The switching voltage regulator may include an inductor for translating energy from one voltage to another, and a capacitor to supply current in times of heavy or transient demands by the integrated circuit. A switch coupling the inductor to a reference plane may enable some of the energy to be drained from the inductor when the ability of the voltage regulator to supply current exceeds the current demand of the integrated circuit.
The power laminate may also include a plurality of decoupling capacitors. In one embodiment, the decoupling capacitors may be surface-mounted capacitors. Mounting the decoupling capacitors on the power laminate may save a significant amount of space on the PCB.
Thus, in various embodiments, the system for distributing power to an integrated circuit including a power laminate may provide various advantages. By distributing power to the integrated circuit using a power laminate, a PCB may be optimized for signal distribution and routing, while the power laminate is optimized for core power distribution. Compromises to both core power distribution and signal distribution that occur when both are implemented on the PCB may be avoided. Placing all power distribution functions on the power laminate, including a voltage regulator circuit and decoupling capacitors may result in a significant savings of space on the PCB. Furthermore, distribution of power by a power laminate may result in a power connection with lower inductance than can be achieved by distributing power on the PCB. This low-inductance power connection may result in a significant lowering of impedance in the power distribution system. With a low impedance power connection, power may flow more easily from the power distribution system to the integrated circuit. In addition, sockets for mounting the integrated circuit and/or the power laminate may be eliminated in those embodiments including a plurality of apertures that allow for the passing of connections between the integrated circuit and the PCB.